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Landfill gas has come a long way from the days when it was simply flared. Now, more landfills are aggressively pumping gas to meet the increasing demand鈥攂ut they need to be sure that they can handle the side effects of their new source of revenue.

Ivan Cooper

 

The waste management sector is finding that landfill gas has shifted from a waste problem to be solved鈥攐ften by just burning the gas onsite鈥攖o being a source of revenue. What鈥檚 driving this trend is a combination of factors:

• Regulatory pressure to reduce greenhouse gas emissions: the methane produced by anaerobic digestion is a potent cause of global warming, Regulators increasingly expect entities that emit GHGs to reduce those emissions, even if it is only by converting the gas to less-damaging carbon dioxide, through flaring.
• Landfill gas-to-energy is now a mature technology, with a wide range of technical solutions available鈥攁nd it is now becoming more practical to significantly increase pumping rates from what was available before.
• There are increasing numbers of third-party companies that will pay the landfill owner for access to the gas the landfill produces, to be burned to produce process heat, or to generate electricity. These companies naturally want to maximize revenue through maximum yield from the landfill.
• Many companies seek to show good environmental stewardship, and using landfill gas in their operations is considered a good thing. A case in point鈥攁 landfill in Ft. Wayne IN, where gas is collected and then used to fire boilers in a nearby GM plant. At other landfills, the gas is used to produce electricity.

Accordingly, the future seems bright for landfill gas extracted at aggressively high rates.

 

The Unwanted Side Effects on Leachate and Condensate from Landfills

However, as a wise person once said, there is no free lunch. Aggressive extraction of landfill gas has been found to have side effects on other aspects of the landfill:

• More wastewater or leachate tends to be produced, if the rate of gas extraction is increased.
• Since the organic materials in the landfill have not had as much time to degrade, the wastewater in the landfill (leachate) tends to become stronger. Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), ammonia and other constituent concentrations such as phenol, Volatile Organic Compounds (VOCs, both chlorinated and non-chlorinated) and PCBs may increase by an order of magnitude or more.
• The extracted gas is treated to remove concentrate, often resulting in further increases of constituents, as has sometimes been observed.

The net result is condensate and leachate that is both greater in volume and higher in constituents that can be harmful to the environment.

 

Don鈥檛 Let Environmental Issues Derail Your Gas-to-Energy Plans

This increased volume and concentration may mean that many landfills seeking to extract gas more aggressively may find a roadblock in their way: the systems and procedures that they have in place to manage leachate and condensate will prove inadequate. While every process has one or more bottlenecks, the landfill owner鈥檚 plans to boost revenue through landfill gas should not be held back by the leachate/condensate management system.

 

This implies that landfill operators and owners need to understand the side effects of aggressive gas pumping, determine if the leachate/condensate system now in place is adequate for the larger volumes and higher constituent loads that can be expected, and, if necessary, develop plans to improve their management systems. Some of the current and emerging areas of concern, for landfill leachate, are:

• Total nitrogen and phosphorus
• Naturally Occurring Radioactive Materials (NORMs)
• Pharmaceutical and personal care chemicals
• Ultra-low metals concentrations
• Nano particles鈥攇enerally defined as particles between 1 and 100 nanometers in size
• Color
• Ultra-violet transmittance
• Whole effluent toxicity failure
• Total dissolved solids
• Boron
• Endocrine disruptors鈥攕uch as chemicals from birth control pills

 

The leachate from a landfill depends on a wide range of factors, including how many wells are in use, whether they are active or legacy wells, and how the landfill operator balances the amount of gas pulled from each well. The age of the landfill has an impact, as does the ambient temperature, the amount of rainfall, and the permeability, depth, temperature and composition of the landfill鈥攈ow much of it is MSW, versus C&D and industrial waste. Aluminum dross has been found to be a particular problem, implicated in subsurface reactions.

 

A Structured Approach Needed for Leachate Treatment

In a paper presented to the WASTECON 2014 conference in Dallas¹ I advocated a structured approach to selecting leachate treatment technologies. As can be seen in Figure 1, there is a wide variety of solutions available, each of which might have a role to play in a specific situation鈥攐r not.

 

Some landfill operators tend to go to equipment manufacturers first, when looking for solutions to leachate management. While equipment vendors are part of this process, their role generally comes more towards the end, when they are asked to provide information on the capabilities of specific pieces of equipment, and later to provide training and trouble-shooting. Often, equipment vendors may push for a specific equipment answer and not be aware of implications to the larger picture.

 

The structured approach starts by working with a qualified professional team whose members are able to carry out a thorough analysis of the situation and recommend which solutions will be best. This team might be from inside the company or external. Often, the best results come from using some personnel from inside the company who are familiar with the way the work is done and the political realities, and external members who may have a broader understanding of how various technology solutions have worked on other sites. A systematic approach involves a multi-stage process:

• Source definition鈥攚ater flow rates, material mass, solute concentrations, expected duration, etc.
• Reliability in meeting effluent goals
• Identification of environmental goals鈥攄ischarge standards, compliance points, and human or ecological risks.
• Identification of applicable technologies鈥攆inding out which technologies are potentially capable of meeting goals.
• Identification of critical parameters鈥攅arly determination of values for parameters that typically drive cost or effectiveness.
• Impartial evaluation鈥攁 feasibility analysis that is completely independent from technology vendors.
• Fatal Flaw Analysis鈥攆inding out if there are any critical factors that prevent implementation.
• Operation Ease
• Capital and O&M costs
• Rating鈥攔elative importance and rating and weighting of factors.
• Head-on-Head Comparison鈥攑air-wise with numerical score.

 

One of the advantages of retaining external professional expertise is that the people involved are likely to have a good understanding of the wide array of leachate treatment solutions available. These can range from passive systems, such as aerobic and anaerobic wetlands and phytoremediation systems using hybrid poplars or willow trees, to higher-maintenance systems, such as biological treatment, reverse osmosis and precipitation processes, or a combination of these.

 

All of these systems have their relative merits. For example, wetland systems may not perform to the standard required during winter months, unless designed for extreme conditions. Other systems may not be optimal in areas where skilled maintenance personnel are required.

 

A structured approach may take longer up front, partly because of the amount of information to be gathered. But it is time well spent鈥攖he solution that is chosen is more likely to be effective at solving the problem, with adequate consideration given to the changing operation of the landfill and to future regulatory changes.

 

Ivan A. Cooper, PE, BCEE, is Principal and National Water/Wastewater Practice Lead for Civil & Environmental Consultants, Inc. Ivan has more than 35 years of experience overseeing projects in wastewater reuse, wastewater permitting and treatability. He has conducted the preliminary and detailed design of more than one hundred industrial and municipal waste treatment and sewage systems. Ivan is a PE in 13 states and is a board-certified environmental engineer from the American Academy of Environmental Engineers with a Wastewater Treatment specialty. He can be reached at (980) 237-0373 or via e-mail at [email protected].

Note

 

1. This article is based on a paper that the author delivered at WASTECON 2014 in Dallas, TX (posted online at ).

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Figure 1

There is a wide range of wastewater management technologies available, and professional expertise can help choosing right combination of technologies given the local situation.

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Landscape of Wastewater Management Technologies

 

• Biological
• Anaerobic
• Aerobic
• Anoxic
• Lagoons
• ASP
• A/O
• Fixed Film
• Immobilized Cell
• UASB
• IFAS
• MBBR
• MBR
• SBR
• Configurations
• 厂贬础搁翱狈鈩�
• 础狈础惭惭翱齿鈩�
• 颁础狈翱狈鈩�
• 顿贰惭翱狈鈩�
• 狈贰搁础顿础鈩�
• BLUE NITE鈩�
• BLUE PRO鈩�
• 叠颈辞蝉迟测谤鈩�
• 翱尝础狈顿鈩�
• 翱搁叠础尝鈩�

 

• Thermal/Evaporation
• Ponds
• Enhanced Ponds
• Waste Heat Evaporators
• MVR
• Multiple Effect
• Crystallizers
• Spray Driers
• Incineration
• Salt Recovery

 

• Miscellaneous
• Electrocoagulation
• Electro-Biochemical
• Air/Stream Stripping
• Organic Sulfide Precipitation
• Deep Well
• Recirculation
• Hyrdoxide Precipiation
• Silica Removal
• Bioaugmentation
• Persulfate Oxidation

 

• Membrane
• UF/MF
• Nano/RO/FO
• Membrane Distillation
• Radial Deionization
• Boutique Membranes/Supports
• Functionalized Membranes
• Ceramic Membranes

 

• Natural Systems
• Constructed Wetlands
• Phytoremediation
• Vetiver
• Trees
• Spray/Drip Irrigation
• Algae Based
• Vertical Biochemical Reactors

 

• Adsorption
• GAC, PAC
• Zeolites
• Ion Exchange
• 厂础惭惭厂鈩�
• ZVI
• GFH
• Activated Alumina

 

• SLS/Dewatering
• Clarifier
• Ballasted Clarifier
• HDS
• Thickeners
• Tank Based
• Rotary Drum
• DAF
• Centrifuge
• Belt Press
• Rotary Press
• Filter Press
• MMF
• Bag Filter

Image courtesy of Civil & Environmental Consultants.

 

Sidebar

Convert Landfill Gas to CNG as Vehicle Fuel?

As part of the shift of landfill gas from 鈥減roblem to be solved鈥� to 鈥渞esource to be exploited,鈥� some landfill operators are working on ways to use the gas as Compressed

Natural Gas (CNG) vehicle fuel. This can have several advantages:

• Cost-savings from being able to displace fuel that would otherwise be bought on the open market
• Landfill gas can be eligible for RIN (Renewable Identification Number) credits
• Public relations and community goodwill that comes from publicizing the use of landfill-generated CNG

 

Landfill operators need to consider a wide range of factors before installing systems to produce CNG, such as whether their vehicle fleet is able to use all the CNG that would be generated, or whether there would be a need to build a pipeline to carry some of the gas elsewhere. As well, they may need to consider whether the RIN program will be available to them long-term. Fueling a vehicle fleet from the landfill鈥檚 own gas emissions may make sound economic sense, as well as demonstrating sustainability in a way the public can easily understand.